Argon Plasma Modification of SU-8 for Very High Aspect Ratio and Dense Copper Electroforming

Abstract

This paper presents a simple but effective method of increasing the wettability of hydrophobic SU-8 grating for use as a copper electroforming template. Untreated SU-8 is hydrophobic; unpatterned SU-8 has a water contact angle of and surface energy of . Argon plasma treatment oxidizes and roughens the surface leading to increased surface energy. For treatment times of or more with plasma power of , the surface energy, roughness, and degree of oxidation plateaus; the water contact angle decreases to ; and the true surface energy increases to after Ar-plasma treatment. Copper electrolyte cannot fill the very high aspect ratio and spatially dense microchannels in untreated SU-8 grating (with water contact angle of ) so that the electroforming circuit remains open. Using a Ar-plasma treatment, the SU-8 grating becomes hydrophilic (with water contact angle of ); this enables a dense copper grating with alternate microwalls and microchannels of aspect ratios of 15.3 and 9.2, respectively, over the entire -diam area to be successfully fabricated from it. This copper mold was used as a mold for UV embossing, demonstrating the feasibility of this technique for the creation of durable molds for mass replication.